This invention relates to coffee makers.
There are various types of coffee maker used for brewing coffee. One type includes a water reservoir which supplies a water duct which is heated by a heating element. The heating process results in the formation of steam in the duct, and the resulting pressure conditions cause hot water to be forced up a riser tube into a coffee filter. Such a system has continuous heating of water in the duct during the brewing process, and this heating system will be referred to as a "continuous heater" in the following description.
Another type of coffee maker comprises a heated water reservoir, and hot water is supplied to a coffee filter under pressure by means of a pump. Espresso coffee machines also use pumped heating systems, and generally operate with higher system pressures.
This invention is equally applicable to all these types of coffee maker.
It is known that the coffee making cycle should be adaptable to the amount of coffee to be made. In particular, an optimum range of brewing times exists which provides a balance between the concentration of the coffee and the flavour. For this reason, the greater the quantity of coffee to be made, the higher should be the flow rate, so that the overall brewing time remains within the desired boundaries.
DE 2839140 discloses a coffee maker having a continuous heater, in which a manual selector is provided for indicating the quantity of coffee to be brewed, and the selection made determines the effective power of the heating element. In a continuous heater,such as that used in DE 2839140, the power supplied by the heating element determines the flow rate up the riser pipe.